We all know the legal limit for drunk driving: Blood alcohol content of .08 percent. That benchmark now applies to all states in the nation. But what about driving without enough sleep? What's the legal limit?

For noncommercial drivers in California — that's probably you — there isn't one. Yet a new AAA Foundation for Traffic Safety report finds that the crash risk for a motorist driving on four to five hours of sleep is “similar” to that of a drunk driver registering .08 blood alcohol content.

For both DUI and drowsy driving cases, there's triple to quadruple the risk of “crash involvement” compared with someone fully sober or well-rested, the AAA report found. But while drivers with .08 or greater blood alcohol content can face jail, nearly $16,000 in estimated court costs and three years of summary probation in California, the same isn't the case for drowsy drivers.

“This is a serious traffic safety problem,” Anita Lorz Villagrana, the Automobile Club of Southern California’s manager of traffic safety and community programs, said in a statement. “Each year, crashes involving a drowsy driver result in injuries and fatalities. Failing to maintain a healthy sleep schedule could mean putting yourself or others on the road at significant risk.”

The bottom line is that people driving on fewer than seven hours of sleep are risking a collision, the report found. “The crash risk associated with having slept for less than four hours is comparable to the crash risk associated with a [blood alcohol content] of roughly 0.12 to 0.15 percent,” according to the report. With only two hours of sleep, motorists are not fit to drive at all, the AAA found.

The report breaks down the increased risk of a collision this way: Six to seven hours of sleep increases the risk of a crash 1.3 times; five to six hours of sleep: 1.9 times; four to five hours of sleep: 4.3 times; less than four hours: a whopping 11.5 times.

Last year a AAA Foundation for Traffic Safety survey found that 41 percent of drivers admitted they had started to nod off or completely fell asleep while behind the wheel at least once in their lives.

The CHP has warned drowsy drivers to “pull over to a safe location to rest or change drivers.”

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